This invention relates generally to turbocharger systems for use with combustion engines. More specifically, this invention relates to a control arrangement particularly for use in controlling the operation of an hydraulic assist turbocharger such as that described in commonly assigned U.S. Pat. No. 4,285,200.
Turbochargers and turbocharger systems in general are known for use in supplying a combustion engine with a charge of air under pressure, commonly referred to as charge air. The turbocharger typically comprises a turbine wheel and a compressor wheel mounted for rotation with a common shaft. The turbine wheel and the compressor wheel are positioned within turbine and compressor housings, respectively, which are in turn secured to a so-called center housing including appropriate shaft bearings for supporting the rotating shaft. Exhaust gases from a combustion engine are coupled for passage through the turbine housing to rotatably drive the turbine wheel, whereby the rotating turbine wheel correspondingly drives the compressor wheel to compress ambient air for supply as charge air to the air intake of the engine.
Turbocharged engines are highly advantageous when compared with conventional naturally-aspirated engines in that substantially denser air is delivered to the combustion chamber or cylinders of the engine. This increased air density results in an increased mass flow of available air for combustion to enable the engine to operate at substantially higher performance levels and with greater efficiency. However, an inherent limitation with turbochargers has been their inability to provide the engine with sufficient charge air during some conditions of engine operation. For example, charge air supplied to the engine by the turbocharger during low speed operating conditions typically is insufficient to permit engine operation at a relatively high load and/or to permit relatively rapid engine acceleration. Moreover, in a two cycle engine, charge air supplied by the turbocharger during starting and/or during other low speed operating conditions normally is insufficient to keep the engine from stalling.
A variety of system concepts are known in the art for boosting or supplementing the normal charge air output of a turbocharger during selected engine operating conditions. For example, auxiliary combustion systems have been proposed wherein the energy level of the engine exhaust gases is supplemented during selected engine operating conditions. Compound turbocharger systems have also been proposed wherein multiple turbine and/or compressor components are coupled together to provide supplemental charge air. Additional system concepts include, for example, mechanical drive trains for mechanically supplementing turbocharger rotation and hydraulic drive systems for hydraulically supplementing turbocharger rotation.
One system concept of particular note is described in detail in U.S. Pat. No. 4,285,200 and comprises a specific hydraulic drive arrangement in the form of a so-called three wheel turbocharger. In this system, a nonventilated hydraulic turbine is carried on a turbocharger shaft between the turbine and compressor wheels, and this nonventilated hydraulic turbine is supplied with hydraulic fluid under pressure to supplementally drive the turbocharger. In this manner, the mass flow output of charge air for supply to the engine is significantly increased during selected operating conditions. However, successful operation of this type of hydraulic drive system is predicated upon the provision of an efficient control arrangement for rapidly supplying the hydraulic turbine with a regulated flow of pressurized hydraulic fluid wherein the fluid flow rate is scheduled in accordance with engine air flow requirements to provide the requisite supplemental driving of the turbocharger. Moreover, it is highly desirable for the control arrangement to unload hydraulic pumping elements when supplemental driving is not required or the need for supplemental driving is reduced such that parasitic hydraulic power losses are minimized.
The present invention provides a control arrangement particularly designed to provide a regulated flow of pressurized hydraulic fluid to the hydraulic turbine of an hydraulic assist turbocharger, wherein the fluid flow rate is controlled in response to engine speed and load and wherein the control arrangement substantially unloads hydraulic pumping elements from the engine when the need for supplemental turbocharger driving is reduced.